This invention relates to a silicone emulsion composition which is adherent to plastic film substrates, and a release film using the same.
In the release paper art, there are known a variety of silicone release compositions for use in preventing any sticking or adhesion between substrates of paper, plastics or the like and pressure-sensitive adhesives. Of these, solvent type silicone compositions have been widely used because of release properties and relatively loose substrate selectivity.
However, from the standpoints of environmental pollution, safety and health, it now becomes necessary to take countermeasures to reduce the amount of solvent used or to recover the solvent to stop discharge to the exterior. One effective means of reducing the amount of solvent used is use of solventless silicone compositions. In order to apply the solventless silicone compositions to paper, laminate paper or plastic film substrates uniformly to a thickness of 1 xcexcm or less, an expensive applicator and a sophisticated technique are necessary. In general, most manufacturers hesitate to accept the change from the solvent type silicone to the solventless type silicone.
Another effective means of reducing the amount of solvent used is use of emulsion type silicone compositions. Silicone compositions of this type are known and used in the art. For example, JP-B 57-53143 discloses a composition obtained by mixing an emulsion composed of an organovinylpolysiloxane, a platinum compound, an emulsifier and water with another emulsion composed of an organohydrogenpolysiloxane, an emulsifier and water. Also known are a silicone composition produced by emulsion polymerization (see JP-A 54-52160), and a composition obtained by emulsifying an organovinylsiloxane and an organohydrogenpolysiloxane with a specific emulsifier and mixing the emulsion with an emulsion of a platinum compound (see JP-A 63-314275).
Since these emulsion type silicone compositions can be diluted with water to any desired concentration, an expensive applicator and a sophisticated technique for thin film coating are not necessary as opposed to the solventless type, and their ease of application is approximate to the solvent type.
However, emulsion type silicone compositions have not enjoyed widespread use because of drawbacks associated with water as the dispersing medium. One drawback is that high temperature cure is necessary due to the latent heat of water for evaporation, indicating poor curability as compared with the solvent and solventless types. Another drawback is that wettability and adhesion to substrates are poor because of the surface tension of water. These drawbacks become serious especially with plastic film substrates.
A number of proposals have been made to solve these problems. For example, JP-A 6-57144 uses an organopolysiloxane having alkenyl radicals at molecular ends, and JP-A 11-222557 discloses blending of an emulsion of a non-silicone polymer. Most of these compositions are intended to apply to paper substrates, and fail to achieve satisfactory adhesion when applied to plastic film substrates.
An object of the invention is to provide a silicone emulsion composition capable of curing into a product effectively adherent to plastic film substrates, and a release film obtained by applying the silicone emulsion composition to a plastic film substrate and curing thereto.
It has been found that a silicone emulsion composition of the addition reaction curing type comprising an organopolysiloxane having at least two alkenyl radicals in a molecule, which contains at least 50% by weight of an organopolysiloxane (I) having the average compositional formula (1), shown below, is effectively adherent to plastic film substrates.
Therefore, the invention provides a silicone emulsion composition of the addition reaction curing type comprising an organopolysiloxane having at least two alkenyl radicals in a molecule, the organopolysiloxane comprising at least 50% by weight of an organopolysiloxane (I) having the following average compositional formula (1). 
Herein R1 is an alkenyl radical, R2 is a monovalent hydrocarbon radical, R3 is hydrogen or an alkyl radical, m and n are positive numbers and p is 0 or a positive number, satisfying 0.6xe2x89xa6(n+p)/mxe2x89xa61.5, and 0xe2x89xa6p/(n+p)xe2x89xa60.05, and m, n and p are such that the organopolysiloxane (I) has a viscosity of 5 to 100 mPaxc2x7s at 25xc2x0 C.